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Concrete In Australia : June 2013
52 Concrete in Australia Vol 39 No 2 FEATURE: BRIDGES provided with a formed gutter to collect surface water and discharge it into a carrier pipe. 5.0 ARTICULATION OF THE AQUEDUCT 5.1 Bearings e superstructure is supported on six pot bearings, two at each pier. All longitudinal environmental and braking forces were transferred to and resisted by the central pier which had fixed and guided bearings. Transverse lateral forces were resisted by one set of guided bearing at each pier. e bearings in the two end piers were designed to take all the longitudinal expansion and contraction movement from thermal, creep and shrinkage effects. After the bridge was launched completely, the aqueduct was lifted 2 mm above its final resting position to remove the temporary launching sliding plates that were connected to the permanent bearings. is final transfer of the aqueduct to the permanent bearings was conducted pier by pier, rather than by lifting the entire structure. VSL developed the lifting methodology which involved four VSL jacks adjacent to the bearings on each pier plinth at a time and moved progressively to the other two piers. Figure 8. (top) Technical drawing of the precast concrete trough. (bottom) Trough as constructed. 5.2 Expansion joint e design and construction of the expansion joint was a critical component of the project. A dual expansion joint was installed at both ends of the aqueduct offering a significant increase in the level of protection from unplanned spills, due to potential failure of a single sealed system, as shown in Figure 9 and Figure 10. e expansion joints were cast onto a 900 mm segment attached to the face of the box section. e design joint allowed movement of ±40 mm per joint. e design was based on a number of prerequisites that must be maintained for the whole life cycle of the aqueduct. e joint was designed to be watertight, corrosion and abrasion resistant, with internal pressure within the pipe to the order of 50 kPa. e HDPE liner was made continuous across the joint. Due to the unique design requirements of the expansion joint, particularly the size, the project team was not able to buy an "off the shelf " item. Developed and designed by the alliance, the aqueduct expansion joint was the world s first dual system adopting the use of two separate seal designs and base materials increasing the safety of the aqueduct. e system will allow operations staff to have one seal in place when performing maintenance on or replacement of the other seal. is system allows flows to always be contained and provides a barrier of separation to live sewage. e system also provides the ability to check for any leakage through taps. 6.0 AQUEDUCT SUBSTRUCTURE 6.1 Precast segmental piers e bridge support and longitudinal stability was provided by three piers placed in line with the original brick piers. Use of precast hollow segmental piers avoided the need for temporary works over the waterways. Precast solution reduced onsite construction tasks and minimised construction times. e piers were designed and constructed using 7.6 m x 2.13 m x 1.8 m segmental units, vertically prestressed with VSL CT stress bars, as shown in Figure 11. Permanent stress bars were connected by couplers and placed in heights rigid enough ensuring pier segments could be erected. e solid top bearing units were connected on top of hollow pier segments and grouted once in place. A minimum 0.25 MPa compressive stress